Paclitaxel (trade name: Taxol) is a diterpenoid compound extracted from Taxus brevifolia barks, with its molecular formula C47H51NO24 and molecular weight 853.92, chemical name: (2S,5R,7S,10R,13S)-10,20-bi(acetoxy)-2-benzoyl-oxy-1,7-dihydroxy-9-oxo-5,20-epoxy taxanes-11-ene-13-radical(3S)-3-benzoyl amino-3-phenyl-D-lactic acid ester. Paclitaxel is a white or similar white crystalline powder, has relatively stable chemical properties at the condition of pH 4˜8. This product has a higher fat-solubility (log P.0/w=3.5), almost insoluble in water. According to different literatures, its solubility in water is within the range of 0.25 μg/ml˜0.60 μg/ml, difficult soluble in many commonly-used pharmaceutical solvents. A number of pharmacological tests show that, paclitaxel has a significant effect on advanced ovarian cancer, metastatic breast cancer and melanoma and has high curative rate on refractory ovarian cancer and metastatic breast cancer, has good prospects on the treatment of prostate cancer, gastrointestinal cancer, small cell lung cancer and non-small cell lung cancer. So it is one of the anti-cancer drugs with the highest anti-cancer effect discovered at present.
Because of difficult absorption through oral taking (oral absorption rate: 2%˜4%), paclitaxel is administered through injection in clinical application. The existing paclitaxel oral injection is prepared into a colorless viscous concentrated solution (containing 30 mg paclitaxel in 5 ml of solution) with polyoxyethylene castor oil and anhydrous alcohol in a ratio of 1:1 (V/V). When using this product, the concentrated solution is firstly diluted into a 500 mL 0.9% sodium chloride injection or 5% glucose injection liquid or 5% dextran injection liquid. After diluted into a solution containing 0.06 mg/ml paclitaxel (solvent content of 0.5%˜1.0%), the mixed solution is added by intravenous infusion for 3˜24 h after filtered through a filter of 0.22 μm diameter.
The infusion dose is 135˜175 mg/m−2 and the maximum tolerance infusion dose is 225˜240 mg/m−2 within 3 h.
Paclitaxel injection uses polyoxyethylene castor oil/anhydrous ethanol as solvent, having a high incidence of clinical allergic reaction. When used, allergic reaction prevention treatment should be conducted by oral administration of 10 mg dexamethasone 12 h and 6 h before drug administration and intramuscular injection of 20 mg diphenhydramine and intravenous injection of 300 mg cimetidine or 50 mg ranitidine 30˜60 min before drug administration. Those patients who have allergic reactions are injected with epinephrine for treatment. In addition, the paclitaxel injection cannot be prepared, stored and injected with PVC plastic containers or injection containers so as to prevent from reaction between solvents and containers, which may generate other allergens. The diluent solution is stored in a glass or polypropylene plastic container or in a special polyester injection device. Although the sensitization mechanism of paclitaxel injection is still unclear, the same allergic reactions occurred in another two drugs (cyclosporine and Teniposide) adopting this solvent and tests also confirmed that castor oil itself can cause dog's histamine release and hypotension (Clinical Oncology, 1994; 6: 40), therefore, the allergenicity of solvent castor oil also becomes the research focus. In recent years, the study of high efficiency and low toxicity of drug carrier containing no castor oil and new paclitaxel administration technology has become the research hot spot.
At present, researches about paclitaxel administration technology mainly focus on liposomes, combined solvents, cyclodextrin, emulsions, nanoparticles, chelation, microspheres and other technologies. Because of the special molecule inclusion function of cyclodextrin and the clinical application of injection cyclodextrin derivatives, researches on cyclodextrin-paclitaxel inclusion technology has made rapid progress. At present, the main types of cyclodextrin used to paclitaxel preparations improvement include: acetyl-γ-cyclodextrin, hydroxypropyl-β-cyclodextrin, hydroxypropyl-γ-cyclodextrin, bridged Bis(β-cyclodextrin), γ-cyclodextrin, succinyl-methyl-β-cyclodextrin, anionic-β-cyclodextrin polymer and so on. Among them, α-cyclodextrin and hydroxypropyl-β-cyclodextrin are the cyclodextrin type materials that have been clinically used to a variety of clinical drug injection preparations, but at present, clinical applications of other cyclodextrins have not been reported yet.
Because of the special structural properties of cyclodextrin and special requirements of paclitaxel application, the valuable cyclodextrin-paclitaxel system should be reflected in such research areas as inclusion reaction, solubilization rate, pharmaceutical stability, chemical stability, paclitaxel activity and side effect changes after inclusion, etc. Although paclitaxel has a larger molecular volume, researches show that cyclodextrin still has a varying degree of inclusion with paclitaxel, and the inclusion reaction degree is directly related to specific reaction conditions such as solvent, temperature, material type especially the type of cyclodextrin structure and proportion of materials, etc. Therefore, different conclusions can be made if taking varying research methods. Thin Layer Chromatography is adopted to determine the changes of Rf values of 23 kinds of anti-cancer drugs before and after adding hydroxypropyl-β-cyclodextrin (inclusion) (International Journal of Pharmaceutics, 1994, 108:69-75) and calculate the migration retention value Rm:Rm=log(1/Rf−1)
Where, Rm stands for the function of drug, mobile phase and cyclodextrin concentration. When its relation curve is extended to zero (no mobile phase and cyclodextrin), the absolute migration retention value Rmo of the inclusion is obtained (if methanol concentration of the mobile phase=0, cyclodextrin concentration=0, then Rm=Rmo, the smaller Rmo is, the greater the change of inclusion migration property is and the greater the inclusion reactions). The results show that, among the 23 drugs, the inclusion reaction of paclitaxel is weakest (maximum Rmo). Further tests with α-cyclodextrin of smaller molecular cavity) showed that, paclitaxel also presented the weakest inclusion ability (Journal of Pharmaceutical & Biomedical Analysis, 1995, 13:533-541); but, the UV spectrum study (Chem. Res. Chinese U. 2005, 21: 749-752) showed that, hydroxypropyl-β-cyclodextrin/paclitaxel in the aqueous solution presented a stronger inclusion reaction, with the inclusion constant up to 3030 M−1, mainly presenting dual inclusion reaction; Phase solubility studies showed that (International Journal of Pharmaceutics, 1996, 133: 191-201), paclitaxel has multiple inclusion with cyclodextrin primarily by dual inclusion, and the dual-inclusion constants of γ-cyclodextrin, hydroxypropyl-γ-cyclodextrin and hydroxypropyl-β-cyclodextrin were 785M−1, 1886M−1 and 7965M− respectively, showing that hydroxypropyl-β-cyclodextrin/paclitaxel has strong inclusion ability. It is also discovered that, after adding organic solvent such as alcohols, the inclusion constants substantially increased and the paclitaxel solubility also significantly improved. In the pure water, cyclodextrin has a better solubilization effect on paclitaxel, and the paclitaxel solubility in about 50% hydroxypropyl-β-cyclodextrin aqueous solution can be up to 3.4 mg/ml (J Pharm Sci, 1995, 84; 1223-1229), which is the best results currently reported. If tetraethylenepentamine bridged bis(β-cyclodextrin) is used, the solubilization of paclitaxel can be up to 2.0 mg/ml (CN1440748). Cyclodextrin solubilization is associated with the proportion of paclitaxel-cyclodextrin in addition to the types of cyclodextrin.
After inclusion, the paclitaxel stability enhanced and its activity has also improved. Fluorescence spectroscopy studies showed that bridged bis(β-cyclodextrin) with cyclodextrin distance of 16.1 Å has an inclusion constant as high as 107M−1 compared with β-cyclodextrin/paclitaxel, and the prepared molecules of ratio of 1:1 was more stable than inclusions but the paclitaxel composition has no changes. After inclusion, the drug-tumor cell reaction time was significantly extended (Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2001, 39: 13-18); Studies showed that, because the increased paclitaxel solubility can improve the extracellular concentration of paclitaxel, conducive to the permeation of drugs through cell membranes, the cyclodextrin solubilization could maintain or enhance the activity of paclitaxel (Bioorganic & Medicinal Chemistry Letters, 2002, 12:1637-1641); After paclitaxel was added to cyclodextrin, a stable preparations solution containing a small amount of organic solvents or additives could be prepared (HU P9701945; CN1281373/ZL98811010.5). In 1:50 cyclodextrin solution, the paclitaxel solubility reached 1.5 mg/ml. The inclusion complex prepared by acetyl-β-cyclodextrin or hydroxypropyl-β-cyclodextrin could significantly reduce the cardiovascular and respiratory side effects of existing paclitaxel preparations (polyoxyethylene castor oil/anhydrous ethanol solvent). Studies also showed that, inclusion reaction could also reduce side effects of paclitaxel itself (U.S. Pat. No. 6,218,374; U.S. Pat. No. 5,804,568). Animal tests showed that, use of paclitaxel inclusion complex injection prepared by hydroxypropyl-β-cyclodextrin could reduce the tissue damages of the injection parts by ⅔ compared with the paclitaxel preparations dissolved in ethanol.
There are a variety of technological inventions on the improvement of paclitaxel injection by using cyclodextrin. CN1589157 (US2005009783) discloses a paclitaxel/hydroxypropyl-β-cyclodextrin composition and the preparation method thereof. For the invention, the paclitaxel was dissolved in ethanol by a ratio of 45 g hydroxypropyl-β-cyclodextrin, 30 mg paclitaxel and 100 ml water, then added to the hydroxypropyl-β-cyclodextrin aqueous solution to prepare inclusion complex. However, a mass ratio of paclitaxel/cyclodextrin as high as 1:1500 is difficult for clinical application; HU P9701945 adopted a lower proportion of cyclodextrin, but the reported solubilization effect was not significant; U.S. Pat. No. 6,284,746 discloses an example, under the example, 11.6 mg paclitaxel and 4 g 2,6-dimethyl-β-cyclodextrin was used to prepare an inclusion complex and the paclitaxel solubilization was up to 0.9-1.0 mg/ml; U.S. Pat. No. 5,684,169 discloses that a high proportion of a variety of cyclodextrins were added with a large amount of organic solvents such as methanol, acetonitrile, ethyl acetate unsuitable for drug use. HU71251 discloses that a variety of cyclodextrins in a molar ratio of 1-20 could only allow paclitaxel solubilization to 0.05 mg/ml; HU65835 discloses that a 20 times of molar ratio (about 31 times of mass ratio) of branched cyclodextrin could allow paclitaxel solubilization to about 0.32 mg/ml.
Although studies on paclitaxel/cyclodextrin inclusion are very active, no paclitaxel/cyclodextrin inclusion is sold in the markets and the safety problems of cyclodextrin is one of the main reasons. At present, it is proved that only three dextrins and cyclodextrin derivatives including α-cyclodextrin, hydroxypropyl-β-cyclodextrin and methyl-butyl-β-cyclodextrin can be used for injection (Expert Opin Drug Deliv, 2005 March; 2(2):335-51). Among the paclitaxel preparation modification studies, more researches focus on hydroxypropyl-β-cyclodextrin, while no researches on sulfobutyl-β-cyclodextrin have been reported. For other cyclodextrins, because of no sufficient safety data, their actual technological applications are relatively higher. The major disadvantages of prior arts are: low solubility of paclitaxel (without significant cyclodextrin solubilization effect), poorer pharmaceutical stability and precipitation after dilution, higher proportion of paclitaxel/cyclodextrin, high proportion of residual organic solvents, too high cyclodextrin concentration failing to meet the basic requirements of paclitaxel preparations, etc. Selection of new cyclodextrin types with excellent performance and carrying out inclusion technology systematic research are the new methods to change such a state.